(a) Field of the Invention
This invention generally relates to a needle-less injector for delivering a dose of liquid into the inner housing of a human or animal. More particularly, but not by way of limitation, to a spring actuated needle-less injection device that delivers a high-pressure jet of fluid through the epidermis of the human or animal.
(b) Discussion of Known Art
The advantage of needle-less injection devices has been recognized for some time. Some of these advantages include the absence of a needle that presents a hazard to healthcare workers, the risk of cross-contamination between humans or animals is reduced, the risk of needle breakage in the tissue of the human or animal is eliminated, the jet is generally smaller than the diameter of a hypodermic needle and thus is less painful than a hypodermic needle.
Because of the well-known advantages of a needle-less injection device, there are many pneumatic or gas actuated needle-less injection devices that are designed to provide multiple doses to patients or animals. Most known needle-less injection devices operate by using a piston to drive the fluid to be delivered though a fine nozzle that creates a small, high pressure stream that penetrates the skin simply due to the high pressure. Multi-dose devices depend on a source of air or working fluid that is used to operate the piston that drives the fluid through the nozzle. Thus, a serious limitation of these devices is that they must have a readily available source of air or other fluid to drive the piston. This makes these devices impractical for use in the field conditions of remote areas and inconvenient in hospitals or clinics.
Because of the disadvantages of injection devices that use high-pressure fluids to drive the piston, a great deal of attention has been given to the development of a spring-powered needle-less injection device. The success of known devices has been limited, however, due to problems associated with safety and reliability. The issues regarding safety generally involve the possibility of accidental discharge of the device. And the problems of reliability generally involve the device's ability to deliver a full, known dose of the liquid being delivered into the animal or human.
Safety issues generally arise in association with devices that have exposed triggers or include a ram or piston driving device that can extend beyond the inner housing of the injector. The risk of using this type of device is similar to the risks associated with the triggers on firearms, and that is the inadvertent pressing of the trigger, causing the accidental or premature firing of the device.
Reliability issues include a broad spectrum of problems. One significant problem is the creation of a suitable jet or stream of fluid and the introduction of this jet on to the skin of the animal or human. Preferably, the jet will be a very fine jet that will impact a section of taught skin at an angle of incidence of preferably 90 degrees. Most of the energy of the stream is used to penetrate the skin when the jet impacts the skin at 90 degrees to the skin. Additionally, by keeping the skin taught prior to delivering the jet of fluid, the skin is not allowed to flex, an thus more of the energy from the jet is used to penetrate the skin rather than deflecting or moving the skin.
Therefore, a review of known devices reveals that there remains a need for a spring-operated injection device that prevents firing until the device is properly positioned against the skin.
There remains a need for a hand-held, spring operated needle-less injection device that will ensure that the skin is held taught and that the nozzle that is to deliver the jet is held at 90 degrees to the skin prior to allowing the jet to be delivered to the skin.